The intake and exhaust valves of an internal combustion engine are operated by camshafts extending the length of the engine. The camshafts are driven by a sprocket attached to the end of the camshaft and a flexible tension-transmitting member such as a belt or chain meshes with the sprocket for driving the camshaft from the engine crankshaft to synchronize the camshaft and crankshaft rotation.
Due to the length of the camshaft and the cyclic resistance to camshaft rotation that occurs as the engine's valves are operated, and due to the vibrations occurring in the belt or chain, an engine camshaft is subjected to many torsional vibrations. One end of the camshaft may be torsionally vibrating about the camshaft axis with respect to the other end of the camshaft or the camshaft may be vibrating as a rigid body causing the chain or belt to stretch and relax, and thereby act as a spring. Either or both such torsional vibrations cause wear in the belt or chain and also produce excessive wear at the cam surfaces. Further, if the engine ignition distributor is driven by the camshaft, as is common, the torsional vibrations within the camshaft will produce excessive distributor gear wear.
The degree of torsional vibration existing in an internal combustion engine camshaft is directly related to the natural frequency of the camshaft and the frequencies being imposed upon the camshaft during the operation of the engine and, usually, these frequencies are above the normal engine operating range. However, should the rotational speed of the engine match the natural frequency of vibration of the combination of the camshaft and belt or chain, torsional camshaft vibration can become very serious and effective apparatus for controlling such camshaft vibration have not been heretofore available.
It is an object of the invention to provide vibration damping means for camshafts of internal combustion engines wherein torsional vibrations may be damped without significantly adding to the cost of the camshaft-related apparatus, nor significantly adding to the size and configuration of the camshaft-related apparatus.
Another object of the invention is to provide a method for damping torsional vibrations occurring within internal combustion engine crankshafts wherein such vibrations may be absorbed by an elastomeric material associated with the camshaft drive sprocket.
A further object of the invention is to provide a drive sprocket for internal combustion engine camshafts which incorporates torsional vibration damping apparatus, and wherein the cost of manufacture of such a drive sprocket is reasonable and may be accomplished with known manufacturing techniques.
Another object of the invention is to provide a system for damping torsional vibrations within internal combustion engine camshafts wherein modifications to the camshafts are not required, the vibration damping structure being incorporated into the camshaft drive sprocket.
In the practice of the invention a typical internal combustion engine camshaft consists of an elongated shaft having a plurality of axially spaced cylindrical surfaces adapted to be supported upon bearings wherein the camshaft rotates about its axis. Intermediate the bearing surfaces a plurality of cams are located which are engaged by valve lifters which control the intake and exhaust valves of the engine. At its end, the camshaft includes a drive sprocket rigidly fixed thereto for rotating the camshaft.
The drive sprocket includes an outer periphery upon which radially extending projections, recesses or teeth are defined which mesh with a flexible tension-transmitting belt or chain which drives the camshaft The belt or chain is usually driven by a sprocket-type member mounted on the engine crankshaft wherein rotation of the camshaft, or camshafts, will be synchronized with the rotation of the engine crankshaft.
A cylindrical surface is defined on the camshaft drive sprocket concentric to the camshaft axis and a metal annular inertia ring is mounted upon this cylindrical surface by a ring of elastomeric material. Preferably, the elastomeric material, which may be rubber, neoprene, or the like, is bonded to the sprocket cylindrical surface and a cylindrical surface defined on the inertia ring. Further, the elastomeric material is preferably under compression as confined between the cylindrical surfaces of the sprocket and inertia ring to increase the mechanical and frictional relationship between the elastomeric material and the sprocket and inertia ring.
Torsional vibrations occurring within the camshaft are also imposed upon the drive sprocket, and as the inertia ring is mounted upon the sprocket by the elastomeric material, such torsional vibrations will be damped by the elastomeric material significantly reducing the magnitude of such vibrations.
The torsional vibrations occurring within the camshaft drive sprocket result from the several torsional forces imposed upon the camshaft, such as due to the natural operating frequency of the engine, the operation of the valve lifters engaging the camshaft cams and the minute stretching and contraction of the belt or chain as it drives the sprocket. The elastomeric material supporting the inertia ring is subjected to all such torsional vibrations, and will effectively reduce the magnitude thereof to reduce wear on the cams, belt or chain, and distributor gearing which may be driven from the camshaft.